We often talk about the struggle of juvenile salmon and steelhead to survive their journey through the Columbia River dams but rarely do we discuss the challenges they face when their journey to the ocean is nearly over. Last month, a group of CRITFC commissioners and staff received an up-close look at one of the largest challenges to juvenile salmon and steelhead: birds in the Columbia River estuary. This stretch of river is a major danger for juvenile fish because of predation by Caspian terns and double crested cormorants at East Sand Island.
East Sand Island is a natural island that was capped off and expanded by the US Corps of Engineers when they dumped material they dredged from the river bottom there. This was part of their effort to keep shipping lanes open for barge traffic. The island is home to tens of thousands cormorants and thousands of terns. East Sand Island is home to one of the world’s largest breeding colonies of both Caspian terns and double crested cormorants. Last year, there were 14,900 breeding pairs of double crested cormorants and 7,400 breeding pairs of terns. With over 45,000 adult birds on East Sand Island foraging for both themselves and their young, the impacts to juvenile salmon and steelhead are significant.
An estimated 20% of the juvenile salmon and steelhead that pass through the Columbia River estuary on their migration to the Pacific Ocean are eaten by these two species alone. This tern and cormorant predation seriously impacts the Columbia Basin’s salmon population. In 2013, the East Sand Island cormorants consumed 16 million juvenile salmonids and the terns consumed another 4.9 million. Annual losses of this size have been occurring since 2011.
With avian predation impacts to salmon and steelhead so significant, the region can no longer afford to ignore the impacts of cormorants and terns on the region’s fisheries population. The equilibrium between predator and prey is out of balance. Measures must be taken to restore the balance between terns, cormorants, and salmon.